In data transmission mode of coordinated multiple points transmission and reception joint process (CoMP JP), multiple cells serve a user equipment (UE) simultaneously, that is, multiple cells send same data to the UE on same time and frequency resources simultaneously. These cells which serve the UE simultaneously compose a coordination cell set, in which a cell is a serving cell, other is a coordination cell.
For example, there are 3 cells which serve a UE simultaneously, and these 3 cells are cell a, cell b and cell c respectively, and the numbers of corresponding antenna ports of the cells are Na, Nb and Nc respectively. In that way, the number of antenna ports serving the UE is Nt, that is: Nt=Na+Nb+Nc. Where specific value of Na, Nb and Nc may be the same or not, for example, Na=4, Nb=4, Nc=4, or Na=4, Nb=2, Nc=2.
In practice, both of a UE and a serving cell need to know the number of a antenna port that serve the UE and a codebook corresponding to a various available rank, for example, rank=1, rank=2, rank=3 and so on, or the number of a_various available layer where the rank or the number of the layers corresponds to the number of the antenna ports. The codebook mentioned herein can support one or more ranks. An available precoding vector or matrix, and the index number corresponding to the precoding vector or matrix, for example PMI and so on, are defined for each supported rank. Afterwards, the UE selects a suitable rank for the use of the UE according to a condition of a channel and a codebook corresponding to a various available rank, and selects a precoding matrix indicator (PMI) from a codebook corresponding to the selected rank, and feeds back the selected rank and the PMI to the serving cell. Then, the serving cell can perform scheduling process according to the received rank and PMI.
In the current technologies, when the number of a antenna port is 1, 2, 4 or 8, a corresponding codebook is definite for a various available rank. In order to facilitate the presentation, when the number of the antenna port is 1, a corresponding codebook can be called as one-antenna codebook; and when the number of the antenna port is 2, a corresponding codebook can be called as two-antenna codebook, and the like.
If the number of the antenna port that serves the UE is not 1, 2, 4 or 8, for example 6, a following codebook generation mode, namely a mode of codebook combination, can be adopted. For example, for any kind of rank, it is to combine any element of a four-antenna codebook corresponding to the rank with any element of a two-antenna codebook corresponding to the rank, which is 4+2 codebook generation mode; or, it is to combine three elements which are arbitrarily selected from the two-antenna codebook corresponding to the rank, which is 2+2+2 codebook generation mode; the other possible modes will not be mentioned one by one repeatedly herein.
In addition, a codebook generated according to different modes will be different, for example, as to any kind of rank, the codebook generated by using the 4+2 codebook generation mode is different from that generated by using the 2+2+2 codebook generation mode.
In the current technologies, a UE with the same number of an antenna port is set to use a same codebook generation mode for any rank. For example, for any rank, different UEs which are served by six antenna ports, need to use the 4+2 codebook generation mode. However, due to different actual situations, for example, conditions of channels are different, when using a certain rank, one UE may be suitable to use 4+2 codebook generation mode, while another UE may be suitable to use 2+2+2 codebook generation mode. Besides, a UE may be suitable to use 4+2 codebook generation mode when using a rank, but may be suitable to use 2+2+2 codebook generation mode when using another rank. If a used codebook generation mode is not suitable, a following used codebook will not be suitable, which will affect the accuracy of PMI obtained by the UE and the scheduling process performed by the serving cell to the UE, and will reduce the system performance.